A fairly inspired redesign of Tic Tac Toe I was surprised to find in a kids' activity book from a local used bookstore.
It gives a small advantage to the odds player, but maybe that's a nice handicap when an adult is playing with a child. Could be mitigated by making the game a four square grid and playing for rows summing to 17 or 19, but maybe that's too much of a spatial departure from Tic Tac Toe. I'm pretty much constantly looking for game design everywhere. I take photos of mazes on playscapes at parks when I'm out with my kiddo and we find a new one. It's pretty cool to find fresh game design in a kids' activity book. Most are page after page of variations on the same few activities.